U.S. Pat. No. 5,565,467 discloses that dutasteride (chemical name: 17β-N-(2,5-bis(trifluoromethyl))phenylcarbamoyl-4-aza-5α-androst-1-en-3-one) of the following Formula (I), a 5-alpha reductase inhibitor, is capable of being used in treating benign prostate hyperplasia, prostate cancer and male pattern alopecia (androgenetic alopecia).

Dutasteride is commercially available as AVODART® soft gelatin capsule (size of 6 oblong) which contains 0.5 mg of dutasteride dissolved in 349.5 mg of a mixture of mono- and di-glyceride of caprylic/capric acid and butylated hydroxy toluene (BHT).
However, in order to fill the active ingredient, dutasteride into the soft gelatin capsule, a large amount of oils and surfactants are required to be used, leading to an increase in the size of the capsule. The large-sized capsule may cause low patient compliance due to patient's inability or unwillingness to swallow the large-sized formulations. In particular, considering that the great majority of benign prostate hyperplasia patients is elderly patients and long-term use of dutasteride is required for the treatment, the large size of the dutasteride capsule leads to disadvantages in that taking such large capsule is very inconvenient for elderly patients and thus patient compliance is low.
Korean Patent No. 10-1055412 discloses a method for preparing a tablet of dutasteride by using a self-emulsifying drug delivery system. However, in order to prepare tablets with improved dissolution characteristics of poorly water-soluble drug, dutasteride, additional excipients such as surfactants and absorbents are needed and the preparation method is somehow complicated as the two-times coating is required. Further, a large amount of absorbents are required, leading to an increase in the size of the capsule which is likely to cause the problem in patient compliance.
Korean Patent Publication No. 10-2013-0086551 discloses a method of improving solubility and bioavailability of dutasteride by using a self-emulsifying drug delivery system. However, a large amount of surfactant (equal to or more than 20% of total composition) is used in the self-emulsifying drug delivery system, thereby causing low stability (decrease in moisture and increase in hardness of gelatin used as a capsule base and the subsequent delayed disintegration and low dissolution rate).
The present inventors of the present invention have conducted a research on formulation of dutasteride to develop a pharmaceutical composition having smaller content in the capsule than that of AVODART® capsule, and having excellent stability even though the amount of the capsule content to be filled is low. They discovered that propylene glycol monolaurate is used as an excellent solubilizer that dissolves dutasteride, thereby causing decrease in the size of the dutasteride capsule, while ensuring an equivalent dissolution rate as that of AVODART®, as well as an improved stability.